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One of the ways we can control the Varroa mite is by breeding bees that actively remove the mites from their colonies themselves. Honeybees are naturally hygienic, and the level of hygienic behavior differs between colonies and between lines of bees. By identifying a trait called “Varroa sensitive hygiene” (VSH), scientists at the USDA have bred a line of bees that can identify mite-infested brood cells and remove them from the colony before mite levels become catastrophic. Using this line of bees, named Pol-line (short for pollination-line), beekeepers can rely less on chemical miticide treatments and reduce their annual colony losses.
The USDA and LSU AgCenter are conducting ongoing experiments to further confirm the efficacy of the Pol-line honeybees as a tool to reduce the impact of Varroa mites. We additionally aim to establish technology transfer programs between the USDA and honeybee breeders and commercial beekeepers to assist them in selecting for and breeding Pol-line colonies and other mite resistant bees.
Pol-line bees were developed by scientists at the USDA-ARS Honeybee Breeding, Genetics, and Physiology Laboratory in Baton Rouge for their enhanced resistance to Varroa mites and favorable commercial beekeeping qualities. Bees were screened for VSH then outcrossed with commercial beekeeping stocks to preserve VSH behavior while also establishing traits such as rapid colony growth, large colony size, queen survivorship, and honey production.
Successful selection of mite-resistant honeybees relies on established breeding techniques. Marker assisted selection (MAS) is a common tool used to select for desirable in other livestock species, but has not been applied to honeybees.
The USDA honeybee research lab in Baton Rouge has been collaborating with multiple groups to finalize the development of a genotyping panel for the suppressed mite reproduction (SMR) trait. Once established, a training program will be developed to share this information with honeybee breeders to teach them how to integrate MAS in their breeding programs.
Selective breeding in honeybees has occurred through crossing of queens and drones with identified desirable traits. In many cases, including with SMR, the process of identifying a desirable trait can be time consuming, especially when screening many colonies. Once established, MAS will reduce the amount of time and manpower required to screen for SMR, greatly increasing breeding capabilities.
Until recently, amitraz-based products were a cheap and effective option for managing Varroa mites, but their widespread use has led to increased levels of amitraz resistance. Scientists at the USDA have developed a field test and target site for genotyping to identify amitraz resistance in a population of mites.
Through field tests and genotyping, USDA and LSU AgCenter extension associates can measure the level of resistance in individual beekeeping operations. This information is imperative for beekeepers to know when and how to shift their mite control strategies.
Additionally, we will be testing different chemical and biological treatments for Varroa to determine regionally specific treatment plans that do not rely on amitraz.
To make informed decisions on Varroa management, we must understand the costs and benefits of different control strategies and how they work in different operations. Treatments are expensive but essential as a lack of treatment will lead to significantly higher colony losses. Weak or dead colonies cannot perform pollination services and must be replaced, costing the beekeepers more than Varroa management.
To understand the economics of Varroa control, collaborators will develop models that consider the costs associated with different management strategies, colony health and losses, and income from colony products and pollination services. We will additionally consider the size and location of individual beekeeping operations to ensure locally relevant economic factors. LSU extension associates will be connecting directly with commercial beekeepers to assess current management practices, understand general beekeeper concerns, and to inform them of a relevant, cost-effective Varroa management plan.
